As people's living standard improves, image-recording devices such as video surveillance devices, camcorders, and cameras with video recording functions are being increasingly used. On such image-recording devices, to take videos less susceptible to the brightness of surroundings, infrared illuminators are often used as supplemental light sources in night or darkness. Besides infrared light, an infrared illuminator also emits a certain amount of visible light. Meanwhile, to turn on an infrared illuminator night and darkness, a light-measuring device is often mounted on the image-recording device to detect the current visible light illuminance and provide a reference for turning on and off the infrared illuminator.
For example, video surveillance devices are used in various occasions. Some of the video surveillance devices include an automatic angle-adjusting function. When a video surveillance device is getting close to the object being filmed or a blocking object (e.g., a wall or a glass cover) is in front of the video surveillance device, the infrared illuminator in the video surveillance device can be turned on. FIG. 1 illustrates the working principles of light-reflection interference in a conventional video surveillance device. As shown in FIG. 1, a blocking object 4 is positioned in front of the video surveillance device 1. When the video surveillance device is located in a relatively dark environment, the light-measuring device in the video surveillance device detects the illuminance of visible light is lower than a preset value, and the video surveillance device 1 turns on the infrared illuminator 3 to provide supplemental light.
However, because the blocking object 4 is in front of the infrared illuminator 3, the supplemental light emitted by the infrared illuminator 3 can be reflected back to the video surveillance device 1. The reflected light can interfere with the light detection of the light-measuring device 2 on the video surveillance device 1. Sometimes, severe interference can cause the video surveillance device to turn on and off the infrared illuminator repeatedly. As a result, the video surveillance device 1 can be damaged, and the images of the video can be adversely affected. The video taken can have impaired quality.